HarryUp

Mitsubishi spec is that the tank heat loss for a 250l tank is 1.5kWh per 24hrs, which equates to about 5 or 6 degrees of water temperature. And that is possibly just measuring the tank, with all the heat conducting copper attached it will be greater. Mine has still lost about 10 or 12 degrees by the time the next HW cycle starts if there has not been a major water draw such as a shower. But I do wonder if the water sitting above the pocket where the thermistor is situated remains more usefully hot whilst the cooling water is also sinking down the tank – even when the reported temperature is tepid the delivered water seems to remain showerworthy hot. If your tank is in an unheated area you should ensure the pipes that enter the tank are as best insulated as you can. I found that after a hot water cycle even the cold water inlet pipe was noticabley warm. And particularly the pipework that forms the hot water heating loop. I had to do it myself as my installers only lagged the easy straighter runs, and it was rather fiddly. I did read somewhere that one installer did not specify Mitsubishi tanks as they had noisy pumps. And this is certainly my experience. Having been concerned beforehand about potential noise from the external unit, I find any noise from that quite bearable as it is mostly a low pitch moving of air. However, one or other, or both, of the circulation and CH pumps fitted to the tank really annoy me. It isn't so much volume as they don't seem too loud even standing right in front of them, but the quality of tone and pitch I find mildly unpleasant and the sound just seems to carry through the walls easily. I haven't really explored implementing a solution yet (sorry!) but I am thinking of trying to get some sound-deadening foam and loosely boxing each pump in.

I am a little late to the thread as I only ended up here after trying to find some explanations for the apparent performance of my own system, and the answers are already here, even if they are a little dispiriting. We have only had our Ecodan PUZ-WM85VAA running for a little over three months so only have limited experience of its performance, and data gleaned from the reporting of the FTC6 controller. (I intend to install some OpenEnergyMonitor monitoring but they are short of supplies at the moment.) I was initially puzzled by the May decline in COP for space heating to the point where it was less efficient than DHW, but the summer setting from the start of June that turns all heating periods off has made the nature of the problem stark – so clear it is a surprise that seems to be little known (perhaps it is specific to the newer models?). To add my small amount of data to the small pool here: in the 21 days since the start of June the HP has drawn 26kWh to deliver 76kWh of heat for DHW, and 38kWh to deliver 0kWh of space heating – which given the amount time it has spent on DHW is pretty low means that it is consuming 1.8kWh per day in standby mode. This doesn't seem to match with the figures that were in the Mitsubishi doc – and presumably would be higher when the weather is colder but the heating is not required. The only relief is that as we have a PV system I suppose a lot of this draw will be met from that rather than grid import. I had delayed considering a PV diverter to see how it would work out over the summer first, but elimating c200+ kWh of unproductive usage by switching the unit off is definitely a reason to consider one.

I'd wondered initially whether the valve was at fault, but the circulation is in the same direction as it should be, i.e. it is the return pipe to the collector that is carrying the heat back up in the evening. I can turn the valve off and stop the flow entirely but then I have to remember to turn it back on first thing, and I've already forgotten once. As a check valve I think it is only going to stop reverse flow? I can't find much info that explains ST systems thoroughly enough to work it out. There are no additional functions enabled on the controller. Nothing so simple...

Our Ecodan SHP was commissioned a couple of weeks ago and was set up with anti-freeze valves and running with no glycol. Which I wasn't expecting! The increased viscosity was mentioned by the installer, along with the orange staining tint should something leak. Glycol will deteriorate in time and the system flushed and refilled with fresh glycol ££ – not quite fill and forget. So, harder work for the circulation pump and requires more effort on part of the HP to deliver the heat. On the other hand the system's anti-freeze mode requires circulation at 20° when external temps fall below 5°, which has been quite a chunk of recent nights. This circulation doesn't count as 'heating' apparently and doesn't appear in the data records, though it must be counted somewhere. I'd like to know how much it costs to run the HP to not heat the house. " No Glycol / Valve - System safe (you can almost forget), system won't restart after disturbance as it will need a fill and flush, £????? for the valve version. (Low Likelihood / Moderate impact) " Why would it need a flush and fill? It would need filling as the valves will have jettisoned some water but then this just requires adding water using the filling loop, no?

Setup: a simple ten-year-old system solar thermal system consisting of a set of roof-mounted evacuated tubes serving a tank on the ground floor with a single pump station on the return line. Last year the system, which had been rather neglected in terms of maintenance, showed signs of erratic performance. I had someone in to service it, they recharged the circulating fluid and also turned the pump down from its highest setting to the medium one. Everything went back to working fine – regular triggering of circulation pump and transfer of heat. Fast forward a few months and I worked out from looking at the logged data that the system had started to lose heat to the collector at night – it was fine before the service but straight after the service this siphoning behaviour has started. Generally, not long after the panels lose the sun and the collector temp has dropped well below the tank temp, the circulation starts – the collector temp rises back up to a few degree below the tank temp and then they gradually both decline in parallel until the next day. The HW tank has recently been replaced to accomodate a heat pump and so the ST has been drained, cleaned well this time, and recharged. The installer wasn't able to offer any specific answers to the siphoning issue other than perhaps the clean would have dislodged some muck that was having an effect. Unfortunately the system does still seem to be siphoning heat. I have failed so far to find a local technician who can help or any relevant information on the internet that is aiding me in understanding how this problem might arise, what failure or lack might be the cause. Perhaps someone here can offer some knowledge to help! If drainback systems are designed to avoid thermal siphoning, what is it in a pumped, pressurised system that prevents unwanted circulation at all? Is it the pump mechanism itself that prevents flow when not operating? A check valve prevents flow in the reverse direction but that is not what is happening here. What it is that has changed in my system that resulted in night time circulation? I have tried adjusting the ball valve above the flow meter that restricts the flow rate to see if that would help, but it doesn't seem to have done so. Any suggestions that I can pass on to whoever I can find to work on the system will be gratefully received.